AN ADAPTIVE SAMPLE-SIZE CUSUM CONTROL CHART

The Cumulative Sum Chart for process control is designed to detect rel atively small shifts in the mean of the process variable. In this pape r, we show that by using samples of two different sizes, rather than a fixed sample, improvements in the chart's ability to detect small shi fts are possible. These improvements are obtained without increasing t he likelihood of a false alarm when the process mean is on target. The average run length values for the adaptive sample scheme are compared to those for a fixed sample scheme for different magnitudes of shifts in the process mean. A fast initial response scheme is presented. An example from a manufacturing process is used to illustrate the advanta ges of the adaptive sampling scheme.